1. Field of the Invention
The present invention relates to a turbo-machine for transporting media charged with solid particles, with one or more impellers disposed inside a housing.
2. Discussion of the Related Art
Turbo-machines can include pumps, turbines, pump-turbines, or the like. They are used in the most various fields of engineering. For a long time, designers have tried to improve the lifetime of these machines which are exposed to wear from abrasive particles.
The first measures for this are generally to use a specially hard and wear-resistant material. For example, in the case of centrifugal pumps, the wheel side spaces and the glands located in these have proven to be areas that are especially sensitive to wear. If the gaps of the glands are enlarged due to wear of the material, increased hydraulic losses will result and, as a consequence of this, reduced efficiency. Furthermore, in the case of multi-stage machines, strong oscillations will result, which can cause the entire unit to break down.
From the European reference EP-B-0 346 677, a way is known to protect the space which receives a shaft seal and a shaft seal itself against wear. This space is located behind the impeller and is separated by a diaphragm gland from the wheel side space, which actually has a higher pressure.
From the German reference DE-A-22 10 556, a centrifugal pump is known in which especially wear-resistant parts, such as the spiral space and the abrasion plates which bound the impeller side space are supposed to improve the lifetime of the machine. Furthermore, by feeding particle-free material into this machine, the wheel side space and also the gland can be protected against abrasive particles.
German reference DE-A-23 44 576 discloses another measure, its design being such that additional transport channels are present in the area of the diaphragm glands. The entries to these transport channels are preceded by a surrounding annular chamber. This measure is supposed to free the transport medium entering the diaphragm gland from abrasive particles. The particles are separated out in the annular chamber, are transported through the transport channels into the wheel side space, and the water liberated thereby then flows to the actual diaphragm gland quasi-free of particles. This measure may indeed be somewhat successful initially, but after a short operating time, the transport channel will become increasingly ineffective. The reason for this is that the particles will become more concentrated in the area of the gland entry, in combination with the after-flowing medium, and wear will thus be accelerated.
Another measure is known from European reference EP-B-O 288 500, where auxiliary blades are affixed on the outside of impeller cover disks. However, annular webs are interspersed among these auxiliary blades so as to reduce the flow of liquid in the impeller side space. But practical tests have shown that this solution also cannot prevent wear.
German reference DE-A-38 08 598 tries to increase lifetime by means of a certain inclination of the surrounding wall surface of the space following an impeller.